Clinical Features

A dental series reported an adverse reaction rate as high as 2.5–10% of all patients receiving local anesthetic injections.
Majority of adverse reactions are not immunologic
- Reactions are usually due to anxiety, vasovagal, psychosomatic responses, excessive dosage, inadvertent injection into a blood vessel, and idiosyncratic responses
- IgE- mediated (type I) allergic reactions are extremely rare and have only been documented in a few case reports

Local Anesthetics

Group 1 Benzoic acid esters--------	Group 2 Amides
Benzocaine Chloroprocaine Cocaine Cyclomethycaine Dimethocaine/Larocaine----- Piperocaine Propoxycaine Procaine/Novocaine Proparacaine Tetracaine/Amethocaine	Articaine Bupivacaine Cinchocaine/Dibucaine----- Etidocaine Levobupivacaine Lidocaine/Lignocaine Mepivacaine Prilocaine Ropivacaine Trimecaine

On the basis of patch testing, group 1 benzoic acid esters cross-react with each other, but they do not cross-react with the group 2 amide drugs. It is not known what relevance this has on immediate-type reactions to local anesthetics.
T.R.U.E. test caine mix patch includes benzocaine, tetracaine, and dibucaine

Appropriate workup remains controversial, patients with positive skin tests often have negative challenges (i.e., high false positive rate), and many positive challenges have subjective symptoms, therefore a challenge test is strongly considered even if skin testing is positive.
Practice parameter
- Allergy testing practice parameter (2008) states that skin testing for diagnosis of local anesthetic allergy is limited by false-positive reactions and that the gold standard for establishing a diagnosis of local anesthetic allergy is the provocative challenge.
- Drug allergy practice parameter (2010) states that to exclude the rare possibility of an IgE-mediated reaction to local anesthetics, skin testing and graded challenge can be performed in patients who present with a reaction history suggestive of possible IgE-mediated allergy to these drugs.
Rarely, preservative used in local anesthetic (e.g. methylparaben) may account for positive skin tests; testing and challenge with pure lidocaine should be considered in these situations
Testing may be done with the local anesthetic suspected of causing the reaction or with a suitable alternative anesthetic that may be used instead

Vital signs and peak flow obtained at the start of the protocol
SPT on the volar surface of the forearm with undiluted preserved local anesthetic without epinephrine
- SPT sites were examined after 15 min; a positive test is defined as a wheal ≥ 3 x 3 mm. Patients with a negative SPT undergo intradermal (ID) testing.
ID skin tests on the volar surface of the forearm with 1:100 dilution of the local anesthetic, injected intradermally to produce an initial wheal of 2 x 2 mm.
- ID sites were examined after 15 min; a positive ID test is defined as a wheal 3 mm greater than the negative control. Patients with negative ID skin testing proceeded to open subcutaneous (SC) challenge.
Open supervised challenge performed in the allergy clinic by initially injecting 0.1 mL of undiluted local anesthetic SC into the upper arm.
- The injection site was examined after 15 min; a positive SC challenge is defined as a wheal 3 mm greater than negative control.
  - If the 0.1-mL challenge was negative, 0.5 mL of undiluted local anesthetic was injected SC into the upper arm at a different location and examined after 15 min.
  - If the 0.5 mL challenge was negative, 1.0 mL of undiluted local anesthetic was injected SC into the upper arm at a different location and examined after 15 min. If negative, the open challenge is negative.
Vital signs and peak flow once again obtained before dismissing the patient

Use lidocaine 1% with methylparaben
SPT with full strength anesthetic then ID skin test with 0.04 ml of 1:100 dilution
- A rare individual will be allergic to methylparaben and will be skin test positive
- If positive skin test, repeat and if still positive, challenge with pure lidocaine (without methylparaben)
SC challenge
- 1 mL saline, then
- 1 mL lidocaine 1% with methylparaben, then
- Challenge with other specific local anesthetics if desired (very low chance of true positive)
- Expect agitation in some individuals with epinephrine containing products

SPT with undiluted local anesthetic
Subcutaneous challenge every 20 min with:
- 0.1 mL 1:100th (1%)
- 0.1 mL 1:10 (10%)
- 0.1, 0.25, 0.5, 1.0 mL (full strength)
Recommend testing with preservatives

SPT with the undiluted anesthetic. If negative..
Successive injections (SC or intradermal) of 0.1 mL of 1:100 dilution, 0.1 mL of 1:10 dilution, and 0.1 mL of full-strength solution are given at 15-minute intervals. If negative...
0.5-1 mL of the anesthetic SC
A placebo step may be added after the SPT and before challenging with the local anesthetic

Protocol
- SPT with full strength local anesthetic, if negative...
- ID with 1:100 dilution, if negative...
- SC injection of saline 1 mL (placebo), then...
- SC with full strength local anesthetic
SC challenge protocol not intended for those rare patients with suspected severe IgE-mediated reactions. A lower starting dose (e.g., 0.1 mL, 1:100) with 10-fold dose increases would be more appropriate.

Dentists and other health care professionals may develop contact dermatitis from local anesthetics
T.R.U.E. test caine mix patch includes benzocaine, tetracaine, and dibucaine